1. Field of the Invention
The present invention relates to a tack label roll for a printing apparatus which conducts printing with a liquid ink. The present invention also relates to a process for producing a printed matter by use of the above tack label roll.
2. Related Background Art
In printing on a tack label or a similar continuous body with an ink-jet head having juxtaposed printing nozzles, a problem is encountered that ink ejection is liable to fail by clogging of the nozzle owing to evaporation of ink at the nozzle tip. To prevent the failure of ink ejection, a method was considered that all of the nozzles of the printing head are used for ink ejection one or more times for every label to print a line at an area where contents of the print are not disturbed, for example, at the top portion or bottom portion of the label. In this method, however, label design is restricted, or label size needs to be larger, disadvantageously.
Another method also considered involved ejecting ink from all of the nozzles intermittently onto an ink recovery cap or the like, not onto a printing label. When the latter method is employed in tack label printing, the cap cannot be placed opposite to the printing head because of the continuous shape of the tack label roll, and therefore the cap or the head has to be moved at the ink ejection onto the cap. Thereby the printing has to be interrupted for this operation, which reduces disadvantageously the throughput of the print per unit time.
The disadvantage results from lack of an ink-absorbing property of the ground paper, i.e., a release sheet backing web, of the tack label. The tack label roll is formed by sticking an overlay paper sheet (i.e., pressure sensitive labels for printing) having adhesive at the back face thereof onto a ground paper sheet (namely, a separator, or releasing paper). The ground paper is made from a material having sufficient releasing property so as to secure the ease of releasing of the overlay paper. Frequently, polyethylene is laminated, or silicone oil is applied on the label side face of the ground paper. Accordingly, liquid ink applied from a nozzle is not absorbed by the ground paper and remains on the surface thereof in a round shape owing to the surface tension. This remaining liquid ink may stain the inside of a printer or neighboring labels, thereby impairing the quality of the printing on the labels on the overlay paper.